A miniaturized drop-based three-electrode system for sensitive electrochemical determination of azathioprine using pencil graphite

Abstract An inexpensive three-electrode system, called a polishable triple graphite electrode, was designed and fabricated using pencil graphite for electrochemical measurement of electroactive compounds. During the manufacturing process, two pencil graphite leads as working and auxiliary electrodes and a silver wire as a pseudo-reference electrode were connected to a special connector and embedded in a Teflon tube. Then, epoxy resin was used to fill the empty spaces between the electrodes. To evaluate the electrode’s performance, the cyclic voltammetry technique was first used in hexacyanoferrate (III)/(II) solution in the presence of KCl supporting electrolyte. Then, the fabricated electrode was used for quantitative analysis of azathioprine in tablet samples using the differential pulse voltammetry technique. Additionally, parameters affecting the analytical performance of the electrode for measuring azathioprine, such as buffer type and pH were optimized. Under the optimized conditions, a linear response was obtained for azathioprine in the concentration range of 5.2-147.2 µM, with a 4.6 µM limit of detection. This three-electrode system offers several advantages, including the capability to measure analytes by dropping the sample solution on the electrode surface, low construction cost due to the use of pencil lead instead of more expensive materials, reduced chemical consumption, and ease of use compared to conventional three-electrode systems. The miniature design of this system facilitates the analysis of small volume samples (in the range of several microliters), which is highly advantageous for the examination of rare or costly biological analytes.